Process for preparing coagulants for water treatment

ABSTRACT

The invention relates to a process for preparing proteins that can act as effective coagulants in the treatment and purification of contaminated water. In particular, the invention relates to a process for extracting coagulant protein derivatives from the seeds of trees from the family Moringaceae. The invention also relates to coagulation protein preparations prepared by the process, and the use of such preparations for the treatment and purification of contaminated water.

This application is the US national phase of international applicationPCT/GB01/01494 filed Apr. 2, 2001 which designated the U.S.

The present invention relates to a process for preparing proteins thatcan act as effective primary coagulants in the treatment andpurification of contaminated water. In particular it relates to aprocess for extracting coagulant protein derivatives from seeds of treeswithin the family Moringaceae and especially those of Moringa oleiferaLam (syns Moringa pterygosperma Gaertn.).

The seeds of Moringa oleifera Lam (hereinafter referred to as Moringa)are utilised primarily to obtain an edible oil, which is extracted usinga mechanical press. The residue from this extraction process is known aspresscake. It has been found that the seeds of Moringa oleifera containwater soluble, low molecular weight, highly basic proteins that can actas primary coagulants in contaminated water treatment. Thecrushed/powdered seed suspensions and presscake, which remains followingoil extraction, have been found to be effective coagulants but theysuffer from the disadvantage that they result in a large amount ofresidual insoluble material which requires disposing of.

The object of the present invention is to provide an extraction processwhich results in the maximum yield of coagulation proteins from Moringaseeds. The extraction process should preferably be suitable for use inless developed countries thereby providing inexpensive coagulantproteins for water treatment.

According to one aspect of the invention there is provided a process forpreparing coagulation proteins from Moringa seeds which comprises thesteps of:

1. treating Moringa seed presscake and/or whole seed inclusive of shellto produce an evenly divided granular powder having for example aparticle size of from 0.5 to 2.5 mm diameter; and

2. adding the granular powder to a complex salt solution, preferably anaqueous solution containing chlorides of calcium (typically 0.5-1.5g/l), magnesium (typically 3.0-5.0 g/l), potassium (typically 0.5-1.0g/l) and sodium (typically 20-30 g/l), in order to leach protein out ofthe powder; and3. separating the protein solution from the remaining solids; and4. precipitating certain organic compounds including proteins, enzymesand carbohydrates, by heating the solution; and5. removing the precipitates from solution and removing excess water toconcentrate the product protein preferably in the form of a suspensionof solids.

The process preferably comprises the additional step of drying theprotein slurry to a moisture content of 15% or less, preferably 10% orless, most preferably 5% or less.

The extraction process is a series of unit operations, each set up toperform an essential step in the extraction of proteins and theirconversion into a state for practical use from the seeds of the Moringaoleifera Lam tree.

The process will be further described with reference to the accompanyingfigures in which:

FIG. 1 is a schematic drawing of the first part of the process; and

FIG. 2 is a schematic drawing of the second part of the process.

The unit operations of the process are taken in sequence.

Size Reduction

The presscake is received as an unevenly sized, randomly agglomeratedgranular material.

This operation consists of a feed hopper (1) from which the presscake isfed at a controlled rate into a mill (2) the design principles of whichare suitable for the presscake.

On leaving the mill the presscake has been converted to an evenlydivided granular powder of a particle size typically 0.5-2.5 mmdiameter, preferably 1-2 mm diameter, and with a minimum of very fineparticles which would reduce the efficiency of a later separationoperation.

The milled product is collected in a receiving hopper (3) incorporatingan exhaust duct for the airflow induced by the mill. The receivinghopper has a device such as a rotary valve to facilitate discharge ofthe product into containers or onto a conveyor (4) for transport to theextraction operations.

Extraction

This consists of one or more process vessels (5) and a facility (7) forproviding a complex salt solution, i.e. typically an aqueous solutioncontaining chlorides of calcium (1 g/l), magnesium (4 g/l), potassium(0.75 g/l) and sodium (24 g/l).

The process vessel is typically a vertical cylindrical tank with a basesloping to a discharge outlet and equipped with a mixer (6) employing apropeller or dispersion type rotating agitator.

In operation, the vessel is filled with the complex salt solution andthe granular powder is added in a specified proportion, typically 20%w/w and thoroughly dispersed.

It is then continuously agitated under ambient temperature conditionsfor a period of time sufficient for the complex salt solution to leachthe protein out of the dispersed powder. Whilst the period of time maybe varied to suit the nature of the powder, approximately 1 hour hasbeen found effective.

At the completion of the leaching operation, the contents of the vesselare in the form of a slurry with spent presscake solids suspended in thesolution of complex salt and extracts.

The slurry is transferred using a positive displacement pump (8) to adecanting centrifuge or a filter press, and most effectively the latter,to separate the solution from the spent powder solids. The spent powderhas a moisture content in the range of, for example, 15-30%. Therecovered solution is collected in holding vessels (10).

Separation of Proteins

From holding vessels (10) the solution of complex salt and extracts istransferred by pump (11) to a system of heat exchangers (12) in whichits temperature is raised above 70° C. and typically to 95° C. for aperiod of between 0.5 and 1 minute. Sufficient agitation, either throughhydraulic or mechanical means, is provided to ensure precipitatedmaterial does not get burnt onto the container surface. The main sectionof the heat exchangers may use steam as an indirect heating medium witha suitable temperature control system for the solution. Optimum energyefficiency is achieved in the primary section of the heat exchangers byusing the outgoing hot solution to indirectly heat the ingoing coldsolution.

During the operation of raising the temperature of the solution above70° C. certain organic compounds (including proteins, enzymes andcarbohydrates) are precipitated to form a solid suspension in thesolution. These materials are a by-product and the suspension isdischarged from the heat exchangers through a separator (13), typicallya centrifuge used for continuous operation of disk-stack design. Theprecipitated materials are collected as a dense slurry or cake and theclarified solution is discharged directly from the centrifuge underpressure to holding vessels (14).

Concentration

From holding vessels (14) the solution is fed to an operation in whichexcess water is removed. This may take the form of a multistage vacuumevaporator or preferably a selective membrane filter commonly known asan ultrafilter (15). The latter method is used when considered desirableto remove low molecular weight solutes from the solution in addition towater and is undertaken using a membrane typically of nominal pore size5,000 Kilo Daltons and a differential pressure typically of 20 psi. Thewhole operation typically makes a 10 fold increase in the concentrationof the product protein. The concentrated product is discharged in theform of a suspension of solids in a saturated solution which istransferred into holding vessels (16).

The concentrated product held in vessels (16) may be packed anddistributed for direct use (as a flocculating agent). Alternatively, itmay be dehydrated in a drying operation fed by a pump (17) from thevessels (16).

Drying

If the process is conveniently located, the protein in the state of athick slurry is available for immediate use (as a water treatment aid).However, it must be assumed that in the form of a large scale efficientfactory it will be remote from the various points of use of the protein.For this major purpose, the state of the protein is changed to that of adry powder in which it is resistant to degradation and is convenient forstorage, transport and use.

This operation includes a system for drying the thick slurry to amoisture content preferably 15% or less and producing the protein in afinely divided form for convenience of use.

Freeze drying is a method which dries the protein to a friable solidwhich breaks up to a fine granular state. The preferred method isspray-drying which dries the protein without unwanted degradation andsimultaneously converts it to a fine powder.

The spray dryer (18) consists of a chamber into which the slurry is fedat a controlled rate by a positive displacement variable capacity pump(17). The slurry is dispersed in the chamber in the form of very smalldroplets by means of an atomiser nozzle or atomiser rotating disk. Alarge volume of air is simultaneously introduced which has been heatedto a temperature typically of 200° C. The method achieves a rapid rateof evaporation of the water component of the slurry without raising theproduct temperature to a damaging level and for this protein thedischarge temperature is limited to 100° C. or less, preferably a rangeof 80°-90°, most preferably a range of 84-87° C.

The final product is discharged at two available locations (20) from thespray drying system via a rotary valve or similar method from which itis filled directly into containers for transport or into a conveyorsystem for transfer to a filling process.

In use, the liquid concentrate is typically diluted 2:1 in clean waterand an applied at doses of 1-20 mg/l (equivalent protein content) forportable water treatment depending on the nature of the water to betreated. For wastewater applications the dose range will be between 5and 50 mg/l (equivalent protein content).

The dry product is prepared as a 5% (w/v) stock solution in clean waterand dosed at similar amounts, based on equivalent protein content, asthe liquid concentrate depending on application.

1. A process for preparing coagulant proteins from seeds of trees of thefamily Moringaceae which process comprises the steps of: a) treatingseed presscake and/or whole seed to produce an evenly divided granularpowder; b) adding the granular powder to a salt solution comprisingchlorides of calcium, magnesium, potassium and sodium to extractprotein, in a solution, out of the powder, c) separating the proteinsolution from any remaining solids; d) precipitating certain organiccompounds by heating the solution, wherein said heating comprisesraising the temperature above 70° C., and wherein said certain organiccompounds comprise proteins, enzymes and carbohydrates; and e) removingthe precipitates from solution and removing excess water to yield andconcentrate said coagulant proteins.
 2. A process according to claim 1,wherein said coagulant proteins are a protein slurry, and whichcomprises an additional step of drying the protein slurry to a moisturecontent of 15% or less.
 3. A process according to claim 1, wherein theseeds are derived from Moringa oleifera Lam.
 4. A process according toclaim 1, wherein the granular powder has a particle size from 0.5 to 2.5mm diameter.
 5. A process according to claim 4, wherein the granularpowder has a particle size of from 1 to 2 mm diameter.
 6. A processaccording to claim 1, wherein the salt solution comprises an aqueoussolution containing chlorides of calcium (0.5-1.5 g/l), magnesium(3.0-5.0 g/l), potassium (0.5-1.0 g/l) and sodium (20-30 g/l).
 7. Aprocess according to claim 1, wherein the protein solution andprecipitated materials are separated by centrifuging.
 8. A processaccording to claim 1, wherein the protein solution is concentrated byfiltration.
 9. A process according to claim 1, wherein the proteinsolution is spray dried.
 10. A process according to claim 1, wherein theprotein solution is freeze dried.
 11. A coagulation protein preparationsuitable for use in the purification of water when prepared according toclaim
 1. 12. A method of treating or purifying contaminated watercomprising: a) obtaining water to be treated or purified, and b)applying to the water a coagulant protein preparation according to claim11.